This invention relates to a method of producing an active antioxydant containing a compound which is derived from sesamolin and has the following structural formula (A) (hereinafter referred to as Compound A): ##STR2## As an active antioxydant derived from sesamolin, sesamol which is obtained by hydrolysis of sesamolin has long been known. Antioxydative activity of sesamol, however, is rather weak. Since sesamol has a small molecular weight, it evaporates at a temperature of about 100.degree. C., and its antioxydative activity is practically nonexistent in the range of cooking temperature from 160.degree. to 180.degree. C. at which, for example, frying is done. Compound A is a naturally-occurring active antioxydant and its presence in Justicia Simplex which is used as a medicinal herb in the Himalayan regions and sesame seeds has recently been reported (for example, in Phytochemistry, 19, 322 (1980)). Methods of obtaining Compound A by extracting and separating it from Justicia Simplex and sesame seeds have been considered but since the content of Compound A is only about 20 ppm in Justicia Simplex and about 15 ppm in sesame seeds, it is economically not feasible to rely on such a simple extraction-separation process on an industrial scale. The present inventors have already disclosed that Compound A can be obtained by hydrolysis of a glycoside extracted from sesame seeds with .beta.-glucosidase (Japanese Patent Application Tokkai No. 59-157173). This method, too, is difficult to apply industrially, however, because the content of Compound A in glycoside is small and complicated operations for partial extraction are required.